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A116703
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Number of permutations of length n which avoid the patterns 231, 4123.
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1
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1, 2, 5, 13, 33, 82, 202, 497, 1224, 3017, 7439, 18343, 45228, 111514, 274945, 677894, 1671393, 4120937, 10160465, 25051354, 61765902, 152288233, 375477484, 925766477, 2282543187, 5627772815, 13875674756, 34211464510, 84350802705
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also number of permutations of length n which avoid the patterns 312, 2341, 3412; or avoid the patterns 132, 1324, 3214, etc.
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LINKS
| Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.
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FORMULA
| G.f.: A(x) = -{(2x^2-2x+1)x}/{3x^3-5x^2+4x-1}
Binomial transform of A000930 starting with offset 1: [1, 1, 2, 3, 4, 6, 9,...]. - Gary W. Adamson (qntmpkt(AT)yahoo.com), Oct 23 2007
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CROSSREFS
| Cf. A000930.
Sequence in context: A005183 A005348 A067676 * A007443 A120925 A086588
Adjacent sequences: A116700 A116701 A116702 * A116704 A116705 A116706
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KEYWORD
| nonn,easy
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AUTHOR
| Lara Pudwell (Lara.Pudwell(AT)valpo.edu), Feb 26 2006
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EXTENSIONS
| Edited by N. J. A. Sloane (njas(AT)research.att.com), Mar 16 2008
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